The endodontic instruments (including files and reamers) are used for cleaning and shaping the root canals of infected teeth. They may be in mode of either rotation or reciprocation in the canal by dentists, either manually or with the aid of dental handpieces onto which the instruments are mounted. Instruments are generally used in sequence (depending on different root canal surgery techniques) in order to achieve the desired outcome of cleaning and shaping. The endodontic instrument is subjected to substantial cyclic bending and torsional stresses as it is used in the process of cleaning and shaping a root canal. Because of the complex curvature of root canals, a variety of unwanted procedural accidents such as ledging, transportation, perforation, or instrument separation, can be encountered in the practice of endodontics.
Currently, endodontic rotary instruments made of Shape Memory Alloys (SMA) have shown better overall performance than stainless steel counterparts. However, the occurrence of unwanted procedural accidents mentioned above has not been drastically reduced. Therefore, it necessitates new endodontic instruments with improved overall properties, especially flexibility and resistance to fracture either due to cyclic fatigue and torsional overload.
U.S. Pat. No. 4,889,487 discusses an endodontic file having one or more elongated, bow-shaped bends for being used to enlarge and shape the root canal. Since not all root canals have the same geometry, a conventional tapered file typically produces a circular cross-section thereby limiting the removing the dentin and soft tissue from the canal to generally one sized canal opening corresponding to the circular-cross-section of the conventional file. This patent discusses crimping the file between to stamping member to shape the file to the desired bend radius. The problem with crimping a file is that the tool used to crimp may potentially damage the fluting of the file thus making less efficient in cutting. Another issue with crimping a file is that it inherently weakens the file in that crimped area thus making it more susceptible to breaking within the canal. U.S. Pat. No. 7,713,059 discusses an instrument for cleaning and/or shaping and/or widening a channel for a root canal. This design having an inner volume enclosed by the instrument and its outer contour may be allowed to change as a result of the forces exerted on it while working.
One possibly advantage of the present invention as compared to conventional rotary files is a method for forming a non-superelastic file. Another possibly advantage of the present invention as compared to conventional rotary files is a method for forming a nonlinear file (e.g., a non-superelastic nonlinear file) that may be able to change shape and geometry by either expanding or collapsing while shaping a root canal. Also, by shaping the rotary file with this process of using a fixture to shape set a shape memory alloy (e.g., NiTi), it may prevent the fluting from being damaged as well as maintaining the geometry throughout the process of preparing a root canal.